The present invention relates to an oscillation circuit having a temperature compensation circuit for compensating a frequency change of an oscillator due to a change in an ambient temperature. In particular, the present invention relates to an oscillation circuit to temporarily stop an oscillation output to output a temperature sensor output of the temperature compensation circuit.
Conventionally, a configuration has been known in which two circuits A and B having different functions and having different input and output pads respectively and the respective input and output pads have therebetween switching switches consisting of transfer gate switches. By controlling the ON and OFF of these switching switches by a signal from a test controller, any one of the two circuits A and B is selected to be operable and an output from the selected circuit is outputted from a test terminal shared by the two circuits or is outputted from the output pad of the circuit. This type of conventional circuit is disclosed in Japanese Unexamined Patent Application Publication No. 2000-155153.
However, the conventional switching switch has a disadvantage as shown below. Specifically, in an OFF status, a parasitic capacitance functions as a bypass path as shown in FIG. 2 and the output from the one circuit A leaks to the other circuit B to cause noise, causing an adverse influence on the operation of the circuit B. This disadvantage is particularly conspicuous when the circuit A is an oscillation circuit having an oscillator of a frequency temperature characteristic changing depending on an ambient temperature and the circuit B is a temperature compensation circuit for supplying a frequency control signal depending on the ambient temperature to this oscillation circuit and thus low noise is required for the circuit B receiving the output leaked from the circuit A. Specifically, a frequency control signal of the temperature compensation circuit is influenced by noise to cause an adverse influence on the operation of a variable capacity diode of an oscillation section to deteriorate the frequency temperature characteristic or to cause phase noise. The conventional design also has another disadvantage in which the input and output pads of the respective circuits A and B occupy a large area in an apparatus accommodating the circuits A and B and thus the reduction of the area in the apparatus is inhibited.